Perpendicular magnetic recording layer with regions having different magnetic anisotropy constants

ABSTRACT

A perpendicular magnetic recording medium and a method of manufacturing the same are provided. The perpendicular magnetic recording medium comprises a recording layer including a plurality of regions formed in the depth direction of the recording layer and a magnetic anisotropy constant of a region relatively deeper than another region, among the plurality of regions, is greater than that of the another region. The method of manufacturing a perpendicular magnetic recording medium includes: forming a recording layer having perpendicular magnetic anisotropy; and irradiating the recording layer with ions.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2007-0052915, filed on May 30, 2007, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Various embodiments disclosed herein are generally directed to aperpendicular magnetic recording medium including a recording layerhaving a plurality of regions with different magnetic anisotropyconstants and a method of manufacturing the perpendicular magneticrecording medium.

2. Description of the Related Art

Magnetic recording methods may be classified into perpendicular andlongitudinal magnetic recording methods. In the longitudinal magneticrecording method, information is recorded by using a characteristic thata magnetization direction of a magnetic layer is aligned in parallelwith a surface of the magnetic layer. In the perpendicular magneticrecording method, information is recorded by using a characteristic thata magnetization direction of a magnetic layer is aligned perpendicularlyto the surface of the magnetic layer. Regarding the recording density,the perpendicular magnetic recording method is more advantageous thanthe longitudinal magnetic recording method. Accordingly, in order toobtain high density in magnetic recording, the perpendicular magneticrecording medium has been continuously researched.

FIG. 1 illustrates a general structure of a conventional perpendicularmagnetic recording medium. Referring to FIG. 1, the perpendicularmagnetic recording medium includes a substrate 10, a soft-magneticunderlayer 12, an intermediate layer 14, and a recording layer 16. Amagnetic field generated from a recording head (not shown) passesthrough the soft-magnetic underlayer 12 and returns to the recordinghead, thereby forming a magnetic path H. At this time, a perpendicularcomponent of the magnetic field magnetizes magnetic domains of therecording layer 16 and records information.

On the other hand, in magnetic recording, the recording density islimited due to a superparamagnetic effect. That is, as the recordingdensity increases, a grain size of the recording medium decreases.Accordingly, thermal stability decreases. When the thermal stabilitydecreases below a predetermined threshold, magnetic moments may not bealigned in one direction due to thermal agitation. The threshold isrepresented as follows:

$\begin{matrix}{{\frac{K_{U}V}{K_{B}T} > 40},} & \lbrack {{Inequality}\mspace{14mu} 1} \rbrack\end{matrix}$where, K_(U) is a magnetic anisotropy constant, V is a grain volume,K_(B) is the Boltzmann constant, and T is an absolute temperature.

Accordingly, in order to manage the increase of the recording density,the thermal stability that satisfies Inequality 1 has to be maintained.In order to maintain the thermal stability, a magnetic recording mediumwith a large magnetic anisotropy constant K_(U) has to be manufacturedso as to have a high anisotropic energy even in a small grain size. Whenthe anisotropic energy of the recording medium increases, the coercivityHc of the recording medium necessarily increases. Accordingly, it isdifficult that magnetization reversal occurs. Thus, writability becomeslow. For example, in order to secure the stability of recorded data forten years in recording of 1000 Gb/in², the required magnetic anisotropyconstant K_(U) is 1.99E7 erg/cc. However, it is difficult for a currentrecording head to record data in a magnetic recording medium having alarge magnetic anisotropy constant K_(U). In order to solve thisproblem, a method of depositing a magnetic thin film having a largemagnetic anisotropy constant K_(U), a magnetic thin film having a smallmagnetic anisotropy constant K_(U), and an intermediate layertherebetween by changing the thickness of the intermediate layer hasbeen tried. However, in this case, materials selectable for a recordinglayer are limited, and thus it is difficult to manufacture a magneticrecording medium by using the aforementioned method. That is, since itis impossible to form the same isolation regions in two differentmagnetic layers, transition noise increases. Accordingly, the signal tonoise ratio (SNR) increases.

SUMMARY OF THE INVENTION

Various embodiments disclosed herein are generally directed to aperpendicular magnetic recording layer of selected ferro-magneticmaterial having a non-uniform concentration of ions diffused therein toprovide a lower first region of the layer with a first agneticanisotropy constant and an upper second region of the layer with asecond magnetic anisotropy constant less than the first magneticanisotropy constant.

According to another aspect of the present invention, a method ofmanufacturing a perpendicular magnetic recording medium comprisesforming a recording layer having perpendicular magnetic anisotropy andirradiating the recording layer with ions.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 illustrates a general structure of a conventional perpendicularmagnetic recording medium;

FIG. 2 illustrates a structure of a perpendicular magnetic recordingmedium according to an embodiment of the present invention;

FIG. 3 is a graph illustrating examples of distribution of ionconcentration for various ion irradiation conditions;

FIGS. 4A to 4C are schematic diagrams illustrating a recording layerwith magnetic anisotropy constants K_(U) according ion irradiationconditions; and

FIG. 5 is a graph illustrating a switching field according to an anglebetween an external magnetic field and an magnetization easy axis ofgrain in the perpendicular magnetic recording medium having thestructures of FIGS. 4A to 4C.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a perpendicular magnetic recording medium and a method ofmanufacturing the same according to an exemplary embodiment of thepresent invention will be described in detail by explaining exemplaryembodiments of the invention with reference to the attached drawings.

FIG. 2 schematically illustrates a structure of a perpendicular magneticrecording medium 100 according to an embodiment of the presentinvention. Referring to FIG. 2, the perpendicular magnetic recordingmedium 100 includes a recording layer 170 having perpendicular magneticanisotropy. The perpendicular magnetic recording medium 100 has astructure such that a soft-magnetic underlayer 130, an intermediatelayer 150 and recording layer are sequentially formed on a substrate110. A protection layer (not shown) protecting the recording layer 170from the outside may be formed on the recording layer 170. A lubricationlayer may be formed on the protection layer so as to reduce abrasion ofthe protection layer.

The substrate 110 may be made of glass, an Al—Mg alloy, magnesium oxide(MgO), silicon (Si), and the like.

The soft-magnetic underlayer 130 may be made of a soft magnetic materialcontaining one or more materials selected from the group consisting ofcobalt (Co), iron (Fe), and nickel (Ni).

The intermediate layer 150 is disposed between the recording layer 170and the soft-magnetic underlayer 130 in order to improve the crystalorientation and magnetic properties of the recording layer 170. Theintermediate layer 150 may be made of an alloy containing one or morematerials selected from the group consisting of ruthenium (Ru),magnesium oxide (MgO), and nickel (Ni).

Information is recorded in the recording layer 170 through perpendicularmagnetization. The recording layer 170 is constructed with a magneticthin film or magnetic multi-layered thin films containing one or morematerials selected from the group with high perpendicular magneticanisotropy consisting of cobalt (Co), iron (Fe), platinum (Pt), andpalladium (Pd). For example, the recording layer 170 may be made of aCoCrPtX-based material. For example, the recording layer 170 includes afirst region 171 with a magnetic anisotropy constant K_(U1), a secondregion 172 with a magnetic anisotropy constant K_(U2), and a thirdregion 173 with a magnetic anisotropy constant K_(U3). A magneticanisotropy constant of a relatively deeper region among the first tothird regions 171 to 173 is greater than that of another region. Thatis, the magnetic anisotropy constants satisfies the conditionK_(U1)>K_(U2)>K_(U3). Here, the recording layer 170 constructed with thethree regions is exemplified. However, the recording layer 170 may beconstructed with one or more number (N) of regions that satisfy thecondition that the magnetic anisotropy constant of the relatively deeperregion is greater than that of another region. The size of each regionis also exemplified. The size of each region can vary based on ionirradiation conditions. In addition, when N is sufficiently large, themagnetic anisotropy constant of the recording layer 170 has anincreasing gradient with respect to the depth in the recording layer170. The magnetic anisotropy constant K_(U1) of the first region 171that is the deepest region in the recording layer 170 has a value thatsecures thermal stability sufficient to obtain desirable recordingdensity. Similarly, when the recording layer 170 has a gradientcharacteristic that the magnetic anisotropy constant increases as thedepth in the recording layer 170 increases, the maximum value of themagnetic anisotropy constant has a value that secures thermal stabilitysufficient to obtain desirable recording density.

Table 1 shows magnetic anisotropy constants required to secure thestored data for ten years as the recording density increases.

TABLE 1 Areal density (Gb/in²) Grain volume (nm³) Required K_(U) (10⁷erg/cc) 100 855 0.19 130 900 0.18 180 704 0.24 250 484 0.34 300 387 0.43450 256 0.65 600 196 0.85 800 116 1.43 1000 83 1.99

A method of forming the recording layer 170 having the aforementionedmagnetic anisotropy constant is described hereinafter. The recordinglayer is made of a material with a sufficiently large magneticanisotropy constant. For example, the recording layer 170 is formed soas to have a magnetic anisotropy constant K_(U) corresponding to thedesirable recording density. Then, the recording layer 170 is irradiatedwith ions. The ion irradiation is performed by using focused ion beam(FIB) equipment. The ions may be nitrogen (N) ions, helium (He) ions,and gallium (Ga) ions. The selection of ions, a dose of ions, energy, ascan method, and the like are controlled so as to obtain a desirablemagnetic anisotropy constant K_(U). FIG. 3 is a graph illustratingexamples of distribution of ion concentration for various ionirradiation conditions. The magnetic anisotropy constant K_(U) islargely decreased at a region with a high ion concentration. Therefore,the ion irradiation condition can be controlled so that the ionconcentration is the highest in the surface side of the recording layer170, for example, so as to satisfy the aforementioned conditionK_(U1)>K_(U2)>K_(U3). The ion irradiation condition can be controlled sothat the value of the magnetic anisotropy constant K_(U) may becontinuously varied or so that two or more regions have differentmagnetic anisotropy constants K_(U). For this, when irradiating therecording layer 170 with ions, the ion energy or dose of ions may beconstant or continuously varied, if necessary. In addition, an ionpenetration depth is controlled by forming a stopping layer on therecording layer 170. The aforementioned processes may be simulated orperformed experimentally. The ion irradiation condition is controlled soas to maintain the magnetic anisotropy direction and reduce thecoercivity.

When irradiating the recording layer 170 with ions, the ions influencelocations of atoms constituting the recording layer 170. Accordingly, amagnetic property of a ferromagnetic material, specifically, anisotropyor bonding strength is sensitively changed due to the rearrangement ofthe atoms. For example, when irradiating cobalt/platinum (Co/Pt)multi-layered films with gallium (Ga) ions, the magnetic property of themulti-layered films is changed. Specifically, when the ion energy is 30keV and when the dose of ions is 5E12 ions/cc, the ion penetration depthranges 6.8 nm to 9.2 nm. The magnetic anisotropy direction of themulti-layered films is maintained, and the coercivity is reduced.

FIGS. 4A to 4C are schematic diagrams illustrating a recording layerwith magnetic anisotropy constants K_(U) according ion irradiationconditions. FIG. 4A shows a recording layer 170′ constructed with asingle region having a magnetic anisotropy constant K_(U) of 1E7 erg/cc.The recording layer 170′ has a conventional structure that is notirradiated with ions and a comparative example to compare with thepresent invention. FIGS. 4B and 4C respectively show recording layersconstructed with two and five regions with different magnetic anisotropyconstants K_(U) which range from 1E6 erg/cc to 1E7 erg/cc.

FIG. 5 is a graph illustrating a switching field according to an anglebetween an external magnetic field and a magnetization easy axis ofgrain of the perpendicular magnetic recording medium having thestructures of FIGS. 4A to 4C. Referring to FIG. 5, the recording layeraccording to the present embodiment has a lower switching field than theconventional structure of FIG. 4A. Accordingly, writability is improved.In addition, the recording layer having five regions with differentmagnetic anisotropy constants has a lower switching field than therecording layer having two regions with different magnetic anisotropyconstants.

As described above, in the perpendicular magnetic recording medium andthe method of manufacturing the same, the recording layer includes aplurality of regions with different magnetic anisotropy constants or hasa gradient in magnetic anisotropy constants by irradiating a recordinglayer having a high magnetic anisotropy constant with ions. Since theperpendicular magnetic recording medium including the recording layerhas high thermal stability and writability, the perpendicular magneticrecording medium may be used as a high density perpendicular magneticrecording medium.

In addition, in the case of manufacturing the perpendicular magneticrecording medium with the aforementioned features by using the ionirradiation method, it is possible to solve a problem in that arecording characteristic is deteriorated when an interface is not neatlyformed in a case where a recording layer is formed by using twodifferent materials, that is, a material with a high magnetic anisotropyconstant K_(U) and a material with a low magnetic anisotropy constantK_(U),

While the perpendicular magnetic recording medium and the method ofmanufacturing the same according to an exemplary embodiment of thepresent invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of the presentinvention as defined by the appended claims.

1. An apparatus comprising a perpendicular magnetic recording layer ofselected ferro-magnetic material having a concentration of implantedions adjacent an upper surface of the recording layer higher than thatdeeper in a thickness direction of the recording layer to establish atleast first and second regions with different respective magneticanisotropy constants.
 2. The apparatus of claim 1, wherein the firstregion has a first magnetic anisotropy constant Ku₁, the second regionis disposed between the first region and the upper surface, and thesecond region has a second magnetic anisotropy constant Ku₂ less thanKu₁.
 3. The apparatus of claim 1, wherein the second region is disposedbetween the first region and the upper surface, and the first regionmaintains thermal stability of the perpendicular magnetic recordinglayer at a predetermined recording density.
 4. The apparatus of claim 1,further comprising a substrate, a soft-magnetic underlayer and anintermediate layer, wherein the recording layer is formed on theintermediate layer.
 5. The apparatus of claim 4, wherein thesoft-magnetic underlayer is made of a magnetic material containing oneor more materials selected from the group consisting of cobalt (Co),iron (Fe), and nickel (Ni).
 6. The apparatus of claim 4, wherein theintermediate layer is made of an alloy containing one or more materialsselected from the group consisting of ruthenium (Ru), magnesium oxide(MgO), and nickel (Ni).
 7. The apparatus of claim 4, wherein therecording layer is constructed with a magnetic thin film or magneticmulti-layered thin films containing one or more materials selected fromthe group consisting of cobalt (Co), iron (Fe), platinum (Pt), andpalladium (Pd).
 8. An apparatus comprising a perpendicular magneticrecording layer of selected ferro-magnetic material having a non-uniformconcentration in a thickness direction of ions diffused therein toprovide a lower first region of the material with a first magneticanisotropy constant and an upper second region of the material with asecond magnetic anisotropy constant less than the first magneticanisotropy constant.
 9. The apparatus of claim 8, in which thenon-uniform concentration of ions diffused in the layer of selectedferro-magnetic material further provides a third region of the materialabove the second region with a third magnetic anisotropy constant lessthan the second magnetic anisotropy constant.
 10. The apparatus of claim8, wherein a magnetic anisotropy constant of the first region has avalue that maintains thermal stability of the perpendicular magneticrecording layer at a predetermined recording density.
 11. The apparatusof claim 8, further comprising a substrate, a soft-magnetic underlayerand an intermediate layer, wherein the recording layer is formed on theintermediate layer.
 12. The apparatus of claim 11, wherein thesoft-magnetic underlayer is made of a magnetic material containing oneor more materials selected from the group consisting of cobalt (Co),iron (Fe), and nickel (Ni).
 13. The apparatus of claim 11, wherein theintermediate layer is made of an alloy containing one or more materialsselected from the group consisting of ruthenium (Ru), magnesium oxide(MgO), and nickel (Ni).
 14. The apparatus of claim 11, wherein therecording layer is constructed with a magnetic thin film or magneticmulti-layered thin films containing one or more materials selected fromthe group consisting of cobalt (Co), iron (Fe), platinum (Pt), andpalladium (Pd).
 15. The apparatus of claim 8, wherein the ions arenitrogen (N) ions or helium (He) ions.
 16. The apparatus of claim 1, inwhich the ions are gallium (Ga) ions.